1. Field of the Invention
The present invention relates to an active vibration noise control apparatus for canceling vibration noise based on an input from a road surface with canceling sounds, and more particularly to an active vibration noise control apparatus for canceling vibration road noise according to an adaptive control process.
2. Description of the Related Art
Active noise control apparatus (hereinafter referred to as “ANC apparatus”) are known in the art as apparatus for controlling acoustics in relation to vibration noise in vehicular passenger compartments. According to a general ANC apparatus, speakers in a vehicular passenger compartment output canceling sounds in opposite phase with the vibration noise to reduce the vibration noise in the vehicular passenger compartment. An error representing a deviation between the vibration noise and the canceling sounds is detected as residual noise by a microphone, which is positioned near the ears of a passenger in the vehicular passenger compartment, and is used to determine the canceling sounds. Some ANC apparatus reduce noise (muffled engine sounds), which is generated in the vehicular passenger compartment as the engine operates (vibrates). See, for example, U.S. Patent Application Publication No. 2004/0247137 (hereinafter referred to as “US 2004/0247137 A1”), Japanese Laid-Open Patent Publication No. 06-083369 (hereinafter referred to as “JP 06-083369 A”), and Japanese Laid-Open Patent Publication No. 2007-216787 (hereinafter referred to as “JP 2007-216787 A”)}.
According to JP 06-083369 A, vibrations of front road wheels are detected by a pickup (1) located near the front road wheels. Canceling sounds for canceling vibration noise caused by vibrations of the front road wheels are generated based on an output signal (reference signal) from the pickup (1). The output signal (reference signal) from the pickup (1) is delayed by a delay circuit (4) depending on vehicle speed. Canceling sounds for canceling vibration noise caused by vibrations of the rear road wheels is generated based on the delayed reference signal (see, for example, Abstract, FIG. 1, and paragraphs [0018] through [0026]).
According to JP 2007-216787 A, vibrations applied from the front road wheels to the vehicle body are detected by acceleration sensors (14, 16) located near the front road wheels. Vibrations applied from the rear road wheels to the vehicle body are estimated based on detected signals from the acceleration sensors (14, 16) and a vehicle speed sensor (26). Canceling sounds are generated and output based on estimated vibrations applied from the rear road wheels to the vehicle body and vibration noise detected by a microphone (30) (see, for example, Abstract and FIG. 1).